Hi All ,
I have an Arduino Nano that won’t power up from the USB port but that is not the question . I have connected a 10 volt DC 500 milliamp adapter to the Vin and ground , Nano powers up fine . Here is the question , will data still pass through USB without causing problems for my laptop ? I think it should be okay but better safe than sorry . Thanks for taking the time to read the message , please let me know if I would be safe to connect data or if I have incorrectly connected the power adapter .
Tom
Nano clones have a Schottky diode in series from the USB power line to the 5V pin of the Nano. If you also connect the external supply, the Nano's voltage regulator will supply 5V to the 5V pin. There should be no problem since the diode will be reverse biased, so no current should flow back into USB. However, it's puzzling that your Nano won't power up from USB, so I'm a little hesitant to recommend anything. But none of that should have any effect on the USB data lines, so I don't see any problem there. Perhaps others will have a different perspective.
Original Nano has the same diode setup. You can see it more clearly here in this re-arranged Nano schematic.
Yes, the diode (if it has not failed in a shorted state) will keep the regulator's 5V from backfeeding into the PC.
The USB Interface chip is powered from the common 5V line, so as long as 5V exists for it, and Gnd is connected t to the PC, the USB interface should work.
TomDuino2017:
I have an Arduino Nano that won’t power up from the USB port but that is not the question.
It sounds very much as if that is the question!
I suggest you do not use "Vin" with the internal regulator if you propose to connect any other 5 V devices. Connect regulated 5 V - such as a USB "Phone Charger" to "5V" and ground.
Thanks ShermanP , CrossRoads and Paul_ B for your replies .
I was feeling confident about connecting to data but Paul _B’s comment has me worried about power so I have removed the 10v connection to Vin and replaced with regulated 5v power supply to 5v pin .
What is the purpose of the Vin pin ? When / why would it be used ?
Tom
Paul's point is that the internal 5V regulator can handle the Nano's needs, but not a lot more than that. So if you have other things that need 5V - sensors, servos, relays, radios, whatever - you can't just power them from the 5V pin of the Nano without making sure it will work (i.e. - the regulator can still maintain the voltage at 5V without getting hot). The safer method is a "real" 5V regulated supply, which powers the Nano and all the other stuff directly.
I'd still like you to figure out why your Nano won't power up from USB. All of us are bothered by that. You should be too.
Thanks ShermanP .
It was a new Nano , didn’t work from the start . What steps would I take to figure out the reason ? It seems my safest solution will be to throw it away and wait for new ones to arrive in mail .
Heh, heh, don't throw it away! 
We - most of us - don't throw things out without at the very least a full forensic. 
Put it aside in a baggie with a note as to what the problem is. When you are much more familiar with Arduinos - and the Nano is the most practical basic type - you can come back to it and figure it all out.
Actually, if it works when you power it up either using "Vin" or direct 5 V connection to "5V" then it is perfectly usable. It will always work if at all, using direct 5 V connection to "5V" because that is the actual supply voltage on the board. It tells us that the diode between the USB port and the 5 Volt line is defective. It could be replaced but you can just use it - as suggested - by powering to the "5V" pin and ground.
Yeah, logically, it should be the case that the diode has failed open, or is missing, or is not soldered properly. On my Nano clones the diode is on the bottom of the board right under the center of the USB connector. With your meter in resistance mode, or diode test mode, a good diode will conduct a little in one direction, but not at all in the other direction. Yours should not conduct at all in either direction. But if it tests normal, then the problem may be in the USB connector, or even the cable. If it was me, I'd just try to find what the problem actually is, just in case the search leads you to something you weren't expecting. But if it turns out to be a bad diode, you can certainly continue to use the Nano if powered from another source, with no harm done. Then sometime down the line, on a future Digikey order, you can get a replacement diode.
Okay , Paul_ _B and ShermanP , you have convinced me to save it from the trash for a future problem solving session . Before bagging it up with a note I will try ShermanP’s suggestion with multimeter . I’ll report back with any info I find .
Your help was much appreciated .
Tom
How do we know the correct installed the ZUSB driver and that it appears in the Device Manager AND that
he selected the correct port ?
(unless he means the led doesn't light)
Hi raschemmel ,
Yes , the LED did not light up but it did when I provided power through Vin . Not using Vin now , I am following Paul_ _B’s suggestion to use 5v pin . I have put a multimeter across the diode as per ShermanP’s suggestion and there is no signal in either direction .
Thanks to all that answered my questions ,
Tom
La selección de los puertos fue la correcta ? Revisa además que el diodo esté soldado correctamente.
Saludos
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